Magnetic resonance imaging apparatus and magnetic resonance imaging method

ABSTRACT

A magnetic resonance imaging apparatus includes a magnetic resonance data acquisition unit and a cerebrospinal fluid image data generation unit. The magnetic resonance data acquisition unit consecutively acquires a plurality of magnetic resonance data for generating a plurality of cerebrospinal fluid image data, each corresponding to a different data acquisition time, after a labeling pulse is applied. The cerebrospinal fluid image data generation unit generates the plurality of cerebrospinal fluid image data based on the plurality of magnetic resonance data.

This application is a division of application Serial No. 12/722,875filed Mar. 12, 2010 (now U.S. Pat. No. 8,427,149 issued Apr. 23, 2013),which claims priority based on Japanese Patent Application Nos.2009-228772 filed Sep. 30, 2009, and 2010-010976 filed Jan. 21, 2010,the entire contents of all of which are hereby incorporated byreference.

BACKGROUND

1. Technical Field

The present exemplary embodiments relate to MRI (magnetic resonanceimaging) which magnetically excites nuclear spin of an object with an RF(radio frequency) signal having the Larmor frequency and reconstructs animage based on NMR (nuclear magnetic resonance) signals generated due tothe excitation. More particularly, the present exemplary embodimentsrelate to a magnetic resonance imaging apparatus and a magneticresonance imaging method that can image CSF (cerebrospinal fluid).

2. Related Art

Magnetic Resonance Imaging (MRI) is an imaging method that excitesnuclear spin of an object set in a static magnetic field with an RFsignal having the Larmor frequency magnetically and reconstructs animage based on NMR signals generated due to the excitation.

In the field of the magnetic resonance imaging, MRA (magnetic resonanceangiography) is known as a method of obtaining an image of a blood flow.An MRI without using a contrast medium is referred to as a non-contrastMRA. As the non-contrast enhanced MRA, an FBI (fresh blood imaging)method that performs an ECG (electrocardiogram) synchronization tocapture a pumping blood flow is ejected from the heart, therebysatisfactorily representing a blood vessel.

In MRA, “labeling” (synonymous with tagging) is performed on blood inorder to better depict a blood vessel. As a method of labeling blood,there is known a time spatial labeling inversion pulse (t-SLIP) method(for example, see Japanese Patent Laid-Open No. 2009-28525). Accordingto the t-SLIP method, a specific blood vessel can be selectivelydepicted using a non-contrast MRA.

FIG. 1 is an explanatory drawing explaining a data acquisition methodusing a conventional t-SLIP method.

In FIG. 1, the abscissa axis indicates time. As illustrated in FIG. 1,according to the t-SLIP method, when a region selective inversionrecovery (IR) pulse is applied as a labeling pulse, the blood in alabeling region is labeled. Then, when a BBTI (Black Blood TravelingTime) has elapsed since the region selective IR pulse is applied,imaging data acquisition is performed. Then, as illustrated in FIG. 1,in order to make dynamic observation on a blood flow, the BBTI ischanged for each data acquisition before imaging is performed. For thisreason, if a large number of different BBTIs with small difference areset, dynamic observation can be made on the blood flow corresponding toa more detailed change in time.

Further, in the t-SLIP method, a method of applying a plurality oflabeling pulses has been devised.

FIG. 2 is a drawing explaining a data acquisition method withapplication of a plurality of labeling pulses using the conventionalt-SLIP method.

In FIG. 2, the abscissa axis indicates time. As illustrated in FIG. 2,according to the t-SLIP method, a plurality of BBTIs can be set to onedata acquisition by applying a plurality of labeling pulses at eachdifferent timing. In addition, the spatial position of applied labelingpulses can also be changed. By doing so, not only various blood vesselsbut also the CSF can be selectively depicted or suppressed.

However, the CSF has no periodicity such as a cardiac cycle and the CSFflow greatly changes for each data acquisition timing. In light of this,from images acquired by the t-SLIP method, it is possible to understanda dynamic behavior of a periodic fluid, but it is difficult tounderstand a dynamic behavior of a non-periodic fluid accurately.

Moreover, when a plurality of labeling pulses are applied, the periodsfrom the application timing of the respective labeling pulse to dataacquisition timing are changed respectively. For this reason, the methodof applying a plurality of labeling pulses cannot generate imagesrepresenting a dynamic fluid behavior of synchronous time.

Furthermore, the CSF is greatly different in flow depending on itsposition. In light of this, the t-SLIP method of performing dataacquisition a plurality of times by changing the BBTI has difficulty infollowing and imaging the CSF whose flow is changed. Moreover, in orderto understand the CSF flow at a plurality of positions using the t-SLIPmethod, imaging needs to be performed at a different timing for eachposition. For this reason, the t-SLIP method cannot allow a wide rangeof CSF flow of synchronous time to be understood.

In addition, in the t-SLIP method, contrast is greatly changed due to achange in the period from the application timing of the labeling pulseto the data acquisition timing. For this reason, in the t-SLIP method,it is very difficult to visually understand a detailed dynamic CSFbehavior from monochrome image in grayscale.

BRIEF SUMMARY

The present exemplary embodiments aim to provide a technology capable ofimaging an image allowing a dynamic behavior of CSF to be betterunderstood without using a contrast medium in magnetic resonanceimaging.

In order to achieve the aforementioned aim, the present exemplaryembodiments provide a magnetic resonance imaging apparatus comprising amagnetic resonance data acquisition unit and a cerebrospinal fluid imagedata generation unit.

The magnetic resonance data acquisition unit consecutively acquires aplurality of magnetic resonance data for generating a plurality ofcerebrospinal fluid image data, each corresponding to a differentacquisition time, after a labeling pulse is applied.

The cerebrospinal fluid image data generation unit generates theplurality of cerebrospinal fluid image data based on the plurality ofmagnetic resonance data so as to correspond to each of the plurality ofmagnetic resonance data.

In order to achieve the aforementioned aim, the present exemplaryembodiments also provide a magnetic resonance imaging method comprisingthe steps of: applying a labeling pulse;

acquiring a plurality of magnetic resonance data for generating aplurality of cerebrospinal fluid image data, each corresponding to adifferent acquisition time, after the labeling pulse is applied; and

generating the plurality of cerebrospinal fluid image data based on theplurality of magnetic resonance data.

According to the aforementioned magnetic resonance imaging of thepresent exemplary embodiments, it is possible to acquire a CSF imageallowing a dynamic behavior of CSF to be better understood without usinga contrast medium.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a chart explaining a data acquisition method by using aconventional t-SLIP method;

FIG. 2 is a chart explaining a data acquisition method with applicationof a plurality of labeling pulses by using the conventional t-SLIPmethod;

FIG. 3 is a block diagram showing a magnetic resonance imaging apparatusaccording to an exemplary embodiment of the present invention;

FIG. 4 is a functional block diagram of the computer 32 shown in FIG. 3;

FIG. 5 is a chart illustrating imaging conditions with pulse applicationunder the t-SLIP method set by the imaging condition setting unit 40illustrated in FIG. 4;

FIG. 6 is a chart illustrating imaging conditions with application ofthe SPAMM pulse set by the imaging condition setting unit 40 illustratedin FIG. 4;

FIG. 7 is a timing chart illustrating pulse sequences with and withoutapplication of the region non-selective IR pulse before the applicationof the labeling pulse, together with recovery processes of thelongitudinal magnetization component Mz of a spin;

FIG. 8 is a flowchart illustrating a flow of imaging a non-contrast CSFimage of an object P by using the magnetic resonance imaging apparatusof the present invention;

FIG. 9 is a chart showing an example of a CSF image imaged by themagnetic resonance imaging apparatus of the present invention;

FIG. 10 is a chart showing an example of distinguishably displayed CSFobtained by performing display processing on the CSF image illustratedin FIG. 9;

FIG. 11 is a chart showing another example of distinguishably displayedCSF obtained by performing display processing on the CSF image imaged bysetting the labeling region to a stripe pattern;

FIG. 12 is a chart showing an example of a distinguishably displayed CSFobtained by performing display processing on the CSF image imaged bysetting the labeling region to a grid pattern;

FIG. 13 is a chart showing an example of a distinguishably displayed CSFobtained by performing display processing on the CSF image imaged bysetting the labeling region to a radial pattern;

FIG. 14 is a chart showing a plurality of CSF images, each correspondingto a different time, displayed in chronological order, when imaging isperformed by acquiring the respiratory gating signal; and

FIG. 15 is a chart showing an example of a plurality of CSF images, eachcorresponding to a different time, displayed in chronological order inthe same manner as in FIG. 14, when monitoring is performed on theabdominal motion.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

A magnetic resonance imaging apparatus and a magnetic resonance imagingmethod according to exemplary embodiments of the present invention willbe described with reference to the accompanying drawings.

(Configuration and Function)

FIG. 3 is a block diagram showing a magnetic resonance imaging apparatusaccording to an embodiment of the present invention.

A magnetic resonance imaging apparatus 20 includes a cylinder-shapedstatic field magnet 21 for generating a static magnetic field, acylinder-shaped shim coil 22 arranged inside the static field magnet 21,a gradient coil 23 and RF coils 24.

The magnetic resonance imaging apparatus 20 also includes a controlsystem 25. The control system 25 includes a static magnetic field powersupply 26, a gradient magnetic field power supply 27, a shim coil powersupply 28, a transmitter 29, a receiver 30, a sequence controller 31 anda computer 32. The gradient magnetic field power supply 27 of thecontrol system 25 includes an X-axis gradient magnetic field powersupply 27 x, a Y-axis gradient magnetic field power supply 27 y and aZ-axis gradient magnetic field power supply 27 z. The computer 32includes an input device 33, a display device 34, an operation device 35and a storage device 36.

The static field magnet 21 is electrically connected to the staticmagnetic field power supply 26 and has a function to generate a staticmagnetic field in an imaging region by using electric current suppliedfrom the static magnetic field power supply 26. The static field magnet21 includes a superconductivity coil in many cases. The static fieldmagnet 21 gets electric current from the static magnetic field powersupply 26 which is electrically connected to the static field magnet 21at excitation. However, once excitation has been made, the static fieldmagnet 21 is usually isolated from the static magnetic field powersupply 26. The static field magnet 21 may include a permanent magnet,which makes the static magnetic field power supply 26 unnecessary.

The cylinder-shaped shim coil 22 is coaxially arranged inside the staticfield magnet 21. The shim coil 22 is electrically connected to the shimcoil power supply 28. The shim coil power supply 28 supplies electriccurrent to the shim coil 22 so that the static magnetic field becomesuniform.

The gradient coil 23 includes an X-axis gradient coil 23 x, a Y-axisgradient coil 23 y and a Z-axis gradient coil 23 z. Each of the X-axisgradient coil 23 x, the Y-axis gradient coil 23 y and the Z-axisgradient coil 23 z is cylinder-shaped and arranged inside the staticfield magnet 21. A bed 37 is arranged inside the gradient coil 23 andthe area inside the gradient coil 23 is an imaging area. The bed 37supports an object (for example, a patient) P. The RF coils 24 include aWBC (whole body coil) built in the gantry for transmission and receptionof RF signals and local coils arranged around the bed 37 or the object Pfor reception of RF signals.

The gradient coil 23 is electrically connected to the gradient magneticfield power supply 27. The X-axis gradient coil 23 x, the Y-axisgradient coil 23 y and the Z-axis gradient coil 23 z of the gradientcoil 23 are electrically connected to the X-axis gradient magnetic fieldpower supply 27 x, the Y-axis gradient magnetic field power supply 27 yand the Z-axis gradient magnetic field power supply 27 z of the gradientmagnetic field power supply 27 respectively.

The X-axis gradient magnetic field power supply 27 x, the Y-axisgradient magnetic field power supply 27 y and the Z-axis gradientmagnetic field power supply 27 z supply electric currents to the X-axisgradient coil 23 x, the Y-axis gradient coil 23 y and the Z-axisgradient coil 23 z respectively so as to generate gradient magneticfield Gx in the X-axis direction, gradient magnetic field Gy in theY-axis direction and gradient magnetic field Gz in the Z-axis directionin the imaging area.

The RF coils 24 are electrically connected to the transmitter 29 and/orthe receiver 30. The transmission RF coil 24 has a function to transmita RF signal given from the transmitter 29 to the object P. The receptionRF coil 24 has a function to receive an NMR signal generated due toexcited nuclear spin inside the object P by the RF signal and give thereceived NMR signal to the receiver 30.

The sequence controller 31 of the control system 25 is electricallyconnected to the gradient magnetic field power supply 27, thetransmitter 29 and the receiver 30. The sequence controller 31 has afunction to storage sequence information describing control informationneeded in order to make the gradient magnetic field power supply 27, thetransmitter 29 and the receiver 30 drive. The aforementioned controlinformation includes motion control information, such as intensity,impression period and impression timing of the pulse electric currentwhich should be impressed to the gradient magnetic field power supply27. The sequence controller 31 also has a function to generate gradientmagnetic fields Gx, Gy and Gz in the X-axis, Y-axis and Z-axisdirections and RF signals by driving the gradient magnetic field powersupply 27, the transmitter 29 and the receiver 30 according to apredetermined sequence stored.

The sequence controller 31 is also configured to receive raw data, whichare complex data obtained through the detection of an NMR signal and A/Dconversion to the NMR signal detected in the receiver 30, and input theraw data to the computer 32.

Therefore, the transmitter 29 has a function to give an RF signal to theRF coil 24 in accordance with the control information provided from thesequence controller 31. The receiver 30 has a function to generate rawdata that are digitized complex number data obtained by detecting an NMRsignal given from the RF coil 24, performing predetermined signalprocessing to the NMR signal detected, and performing A/D conversion tothe NMR signal after the predetermined signal processing. The receiver30 also has a function to give the generated raw data to the sequencecontroller 31.

The computer 32 gets various functions by the operation device 35executing some programs stored in the storage device 36 of the computer32. Alternatively, some specific circuits having various functions maybe provided with the magnetic resonance imaging apparatus 20 instead ofusing some of the programs.

FIG. 4 is a functional block diagram of the computer 32 shown in FIG. 3.

The computer 32 functions as an imaging condition setting unit 40, asequence controller control unit 41, a k-space database 42, a CSF imagegenerating unit 43 and a display processing unit 44.

The imaging condition setting unit 40 has a function to set an imagingcondition including a pulse sequence based on instruction from the inputdevice 33 and to provide the set imaging condition to the sequencecontroller control unit 41. Especially, the imaging condition settingunit 40 has a function to set a pulse sequence to acquire a CSF imagewithout using a contrast medium. More concretely, the imaging conditionsetting unit 40 has a function to set a sequence for selectivelydepicting a non-periodic CSF by labeling.

Labeling for identifying (distinguishing) a CSF can be performed byapplying a labeling pulse to the CSF or a region of interest. As thepulses available as the labeling pulse, a t-SLIP, a saturation (SAT)pulse, a SPAMM (spatial modulation of magnetization) pulse, and a DANTE(delays alternating with nutations for tailored excitation) pulse areknown.

The t-SLIP includes a region non-selective IR pulse and a regionselective IR pulse. Note that the region non-selective IR pulse can beswitched on/off. The labeling region where a region selective IR pulseis applied can be arbitrarily set independently of an imaging region.Note that the imaging condition may be set so as to apply a plurality oft-SLIPs.

A region selective 90° SAT pulse is obtained by bending a magnetizationvector in a selected slab region by 90° to saturate longitudinalmagnetization. Note that the imaging condition may be set so as to applynot only a single but also a plurality of region selective 90° SATpulses. When the plurality of region selective 90° SAT pulses areapplied and a plurality of selective slab regions can be set to a radialor stripe-shaped pattern.

The SPAMM pulse is also called a rest grid pulse and was originallydeveloped to monitor cardiac motion. The SPAMM pulse is aregion-non-selectively applied pulse, and can form a region saturatedwith a desired pattern such as a stripe pattern, a grid pattern (latticeshaped pattern), and a radial pattern by adjusting a gradient magneticfield. The saturation pattern functions as a position marker, and thusan image showing a CSF flow can be obtained by imaging with applicationof the SPAMM pulse.

The DANTE pulse is also a labeling pulse for forming a region saturatedwith a desired pattern such as a stripe pattern, a grid pattern, and aradial pattern. The SPAMM pulse and the DANTE pulse each are a pulseequivalent to a plurality of SAT pulses applied at the same time.

Further, the imaging condition can be set so that a combination of asingle t-SLIP or SAT pulse or a plurality of t-SLIPS or SAT pulses withthe SPAMM pulse or the DANTE pulse can be applied as the labeling pulse.

FIG. 5 illustrates imaging conditions with application of the t-SLIPpulse set by the imaging condition setting unit 40 illustrated in FIG.4.

In FIG. 5, the abscissa axis indicates time. As illustrated in FIG. 5,after the t-SLIP is applied, data acquisition is consecutively(continuously) repeated a plurality of times DATA ACQUISITION 1, DATAACQUISITION 2, DATA ACQUISITION 3, and so on). Consequently, time-seriesdata at a different time continuous in terms of time such as t11, t12,t13, and so on can be acquired. In other words, imaging data of aplurality of frames, each corresponding to a respective imaging time,are acquired after application of a labeling pulse.

More specifically, according to the conventional technique, asillustrated in FIG. 1, labeling is performed and then data of one frameis acquired, and then labeling is performed again and then data ofanother frame is acquired, and this operation is repeated. Consequently,according to the conventional technique, the labeled CSF is differentfor each frame. In contrast, according to the present invention, asillustrated in FIG. 5, labeling is performed once, and then dataacquisition corresponding to each frame of CSF image is consecutivelyperformed. Thus, the labeled CSF is the same for each frame. Therefore,the CSF image acquisition method according to the present inventionallows the dynamic CSF behavior to be understood more accurately andcontinuously in terms of time.

When a region non-selective IR pulse is turned on, the regionnon-selective IR pulse and a region selective IR pulse are applied atapproximately the same time. The period t11 from the application timingof the t-SLIP to the acquisition timing of the first data can beappropriately set according to the imaging conditions such as a settingposition of a labeling region by the region selective IR pulse, asetting position of a region of interest for depicting the CSF, alongitudinal magnetization relaxation time in a background portion.

The imaging by the t-SLIP method includes a flow-in method and aflow-out method. The flow-in method is to depict unlabeled CSF flowinginto a region of interest from outside the region of interest byapplying the region selective IR pulse to the region of interest toinvert the longitudinal magnetization in the region of interest. Incontrast, the flow-out method is to selectively depict labeled CSFflowing into a region of interest from the labeling region by applyingthe region non-selective IR pulse to invert the longitudinalmagnetization as well as by applying the region selective IR pulse tothe labeling region to invert the longitudinal magnetization of the CSFinside the labeling region to a positive value. In other words, in theflow-in method, the labeling region is set inside the region ofinterest; while in the flow-out method, the labeling region is setoutside the region of interest.

For this reason, the data acquisition timing can be determined so thatthe data acquisition starts after the CSF flows into the region ofinterest. If the longitudinal magnetization of the background portion isinverted by the region non-selective IR pulse, the data acquisitiontiming may be determined so that the data acquisition starts at a timingwhen the absolute value of the longitudinal magnetization of thebackground portion becomes around zero by longitudinal relaxation.

Such a method of using the t-SLIP as the labeling pulse is effective,especially when the magnetic resonance imaging apparatus 20 can generatea high magnetic field equal to or greater than 3T and a relaxation timefor determining tag duration time is long.

FIG. 6 illustrates imaging conditions with application of the SPAMMpulse set by the imaging condition setting unit 40 illustrated in FIG.4.

In FIG. 6, the abscissa axis indicates time. As illustrated in FIG. 6,after the SPAMM pulse is applied, data acquisition is consecutively(continuously) repeated a plurality of times (DATA ACQUISITION 1, DATAACQUISITION 2, DATA ACQUISITION 3, and so on). Consequently, time-seriesdata continuous in terms of time such as t21, t22, t23, and so on can beacquired. Thus, the same advantage as case of applying the t-SLIP can beobtained.

The SPAMM pulse includes an RF pulse and a modulated gradient pulse.FIG. 6 illustrates an example of the SPAMM pulse which is configured byproviding the modulated gradient pulse between the two 90° RF pulses.The width of the stripe pattern and the grid pattern can be controlledby adjusting the waveform and the application axis of the modulatedgradient pulse. A wide pattern formed by application of the SPAMM pulsemoves with the CSF flow. Consequently, if the SPAMM pulse is used as thelabeling pulse, it is possible to obtain a CSF image capable ofobserving a dynamic CSF behavior in a wide range at the same imagingtime. Moreover, since the pattern moves with the CSF flow, the periodt21 from the application timing of the SPAMM pulse to the acquisitiontiming of the first data can be shortly set, so that the period t21becomes substantially zero.

Note that the grid pattern takes about double application time oflabeling pulse of the stripe pattern. The radial pattern takes moreapplication time of labeling pulse than the grid pattern. Therefore, itis preferable that a desired pattern such as a stripe pattern, a gridpattern, and a radial pattern is selected as the pattern of the labelingregion according to the imaging purpose and imaging conditions.

Note that in FIGS. 5 and 6, any sequence such as an SSFP (steady statefree precession) sequence and a FASE (Fast ASE: fast asymmetric spinecho or fast advanced spin echo) sequence can be used as a sequence foracquiring imaging data.

If the timing of applying the labeling pulse such as the t-SLIP, the SATpulse, the SPAMM pulse, and the DANTE pulse is determined based on atrigger signal, any signal such as a biological signal, an ECG(electrocardiogram) signal, a respiratory gating signal by a respiratorysensor (respiratory gating), and a PPG (peripheral pulse gating) signaland a clock signal can be used as the trigger signal. When the ECGsignal or the PPG signal is used, an ECG unit or a PPG signal detectionunit is connected to the magnetic resonance imaging apparatus 20.

It is desirable to display information on “which time phase ofrespiration or heartbeat imaging time of each frame corresponds to” inparallel with each frame, when the respiratory gating signal and(or) theECG signal of an object P are (is) acquired at the same time of imagingdata acquisition and CSF images are displayed after this imaging. If therespiratory gating signal is used, it is preferable that the periodrequired to acquire imaging data of one frame (period of the DATAACQUISITION 1 in FIGS. 5 and 6) should be sufficiently short withrespect to a cycle of respiration. If the cycle of respiration is aboutseconds, it is preferable that the period required to acquire imagingdata of one frame should be, for example, equal to or less than 0.3second.

Likewise, it is desirable to display information on “which time phase ofbody motion imaging time of each frame corresponds to” in parallel witheach frame, when the body motion at a predetermined position such asabdominal expansion and contraction by respiration is monitored at thesame time of imaging data acquisition and CSF images are displayed afterthis imaging. In this case, it is also preferable that the periodrequired to acquire imaging data of one frame should be sufficientlyshort as compared with a cycle of body motion.

Before the labeling pulse such as the SPAMM pulse and the DANTE pulse isapplied, the region non-selective IR pulse may be applied. This isbecause the period, in which CSF is observable, is considered to belonger as described below.

FIG. 7 is a timing chart illustrating pulse sequences with and withoutapplication of the region non-selective IR pulse before the applicationof labeling pulse, together with recovery processes of the longitudinalmagnetization component Mz of a spin. In FIGS. 7A to 7D, the abscissaaxis indicates elapsed time t. In FIGS. 7B and 7C, the vertical(longitudinal) axis indicates longitudinal magnetization component Mz.Here, as an example, the SPAMM pulse as a saturation pulse is used asthe labeling pulse.

FIG. 7A illustrates a pulse sequence when the region non-selective IRpulse is applied before the application of the labeling pulse. FIG. 7Billustrates a recovery process of the longitudinal magnetizationcomponent Mz following the pulse sequence illustrated in FIG. 7A. Forease of comparison between the differences in recovery process of thelongitudinal magnetization component Mz, FIG. 7C is provided under FIG.7B, which illustrates a recovery process of the longitudinalmagnetization component Mz when the region non-selective IR pulse is notapplied. FIG. 7D illustrates a pulse sequence when the regionnon-selective IR pulse is not applied before the application of thelabeling pulse. The recovery process of the longitudinal magnetizationcomponent Mz illustrated in FIG. 7C follows the pulse sequenceillustrated in FIG. 7D.

When the region non-selective IR pulse is not applied, as illustrated inFIG. 7C, the longitudinal magnetization component Mz of the CSF labeledby the SPAMM pulse is gradually returned to the magnetostatic fielddirection from a state of being bent 90°. Here, when the difference insignal level of the NMR signal between labeled CSF and unlabeled CSF isa predetermined value or more, namely, when the difference inlongitudinal magnetization component Mz between the aforementioned twotypes of CSF is a predetermined value or more, the two types of CSF areconsidered to be distinguishable (observable). Thus, when the regionnon-selective IR pulse is not applied, the data acquisition period, inwhich CSF is observable, is as indicated by Δt-observe 2 in FIG. 7C.

In contrast, when the region non-selective IR pulse is applied, thelongitudinal magnetization component Mz of the unlabeled CSF is invertedby 180° after the application of the region non-selective IR, and thenrecovers to the static magnetic field direction, with the elapse oftime, as illustrated in FIG. 7B. Then, as illustrated in FIG. 7B, theCSF labeled by the SPAMM pulse after the application of the regionnon-selective IR pulse recovers the longitudinal magnetization componentMz of the spin to the magnetostatic field direction by 90°. For thisreason, the longitudinal magnetization component Mz of the labeled CSFis recovered to the magnetostatic field direction earlier than that ofthe unlabeled CSF. Subsequently, with the recovery of the longitudinalmagnetization component Mz of the unlabeled CSF, the CSF can be observeduntil the difference in longitudinal magnetization component Mz betweenthe labeled CSF and the unlabeled CSF reach a predetermined value. Inthis case, the data acquisition period, in which CSF is observable, isas indicated by Δt-observe 1 in FIG. 7B, which is longer than Δt-observe2 in FIG. 7C. Therefore, when the region non-selective IR pulse isapplied before the application of the labeling pulse, the period inwhich CSF is observable becomes longer.

When the region non-selective IR pulse is applied before the applicationof the labeling pulse as described above, in the process of processingthe NMR signal and generating image data, it is preferable to performREAL reconstruction processing using the real part (not absolute value)of a magnetic resonance signal which is a complex signal.

More specifically, when the region non-selective IR pulse is appliedbefore, the longitudinal magnetization component Mz of the NMR signal isa negative value in the initial stage of data acquisition. In contrastto this, when a general image reconstruction is performed, for example,the square root of the sum of ‘the square of the real part’ and ‘thesquare of the imaginary part’ becomes a luminance level as the absolutevalue. In this case, both the NMR signals corresponding to itslongitudinal magnetization component being −1 and 1 become equal interms of luminance, and the luminance of each NMR signal is displayed inthe range of 0 to 1.

Meanwhile, when the NMR signal whose longitudinal magnetizationcomponent is a negative value (e.g., −1) is processed as the negativevalue by the REAL reconstruction processing and a predetermined signallevel (corresponding to a longitudinal magnetization component of 1) isadded to the NMR signal, the luminance level of the NMR signal can bedisplayed in the range of 0 to 2. In other words, the dynamic range canbe larger than the case without the REAL reconstruction processing.

Next, the other functions of the computer 32 will be described.

The sequence controller control unit 41 has a function to instruct thesequence controller 31 to perform drive control by providing imagingconditions including a pulse sequence based on information from theinput device 33. In addition, the sequence controller control unit 41has a function to receive raw data from the sequence controller 31 andto store the data as k-space data in a k-space formed in the k-spacedatabase 42.

The CSF image generating unit 43 has a function to obtain the k-spacedata from the k-space database 42, and to generate time series CSF imagedata by performing data processing including image reconstructionprocessing.

The display processing unit 44 has a function to perform displayprocessing such as coloring of the CSF portion on the CSF image data andhas a function to display the CSF image on the display device 34 afterthe display processing.

(Operation and Behavior)

Next, the operation and the behavior of the magnetic resonance imagingapparatus 20 will be described.

FIG. 8 is a flowchart illustrating a flow of imaging a non-contrast CSFimage of an object P by using the magnetic resonance imaging apparatus20 illustrated in FIG. 3.

First, in step S1, the imaging condition setting unit 40 sets the CSFimaging conditions for performing consecutive data acquisition after thelabeling pulse is applied, as illustrated in FIGS. 5, 6 and 7A or 7D (inthe case of FIG. 7A, also set the imaging condition of the regionnon-selective IR pulse applied before the labeling pulse). As thelabeling pulse, the t-SLIP, the SAT pulse, the SPAMM pulse or the DANTEpulse may be used.

Then, in step S2, imaging scan is performed on the CSF according to theset imaging conditions.

The object P is set on the bed 37 in advance. Then, a static magneticfield is formed in an imaging region inside the static magnetic fieldmagnet 21 (superconducting magnet) excited by the static magnetic fieldpower supply 26. In addition, electric current is supplied from the shimcoil power supply 28 to the shim coil 22, and thereby the staticmagnetic field formed in the imaging region is made uniform.

Then, when the sequence controller control unit 41 receives a scan startinstruction from the input device 33, the sequence controller controlunit inputs the imaging conditions including the pulse sequence acquiredfrom the imaging condition setting unit 40 to the sequence controller31. The sequence controller 31 drives the gradient magnetic field powersupply 27, the transmitter 29, and the receiver 30 according to theinputted pulse sequence, thereby a gradient magnetic field is formed inthe imaging region, where the object P is set, and an RF signal isgenerated from the RF coil 24.

Then, an NMR signal generated by nuclear magnetic resonance (NMR) insidethe object P is detected by the RF coil 24 and inputted to the receiver30. The receiver 30 receives the NMR signal from the RF coil 24,performs required signal processing and then A/D conversion on thereceived NMR signal to generate raw data, which is digital data of theNMR signal. The receiver 30 inputs the generated raw data to thesequence controller 31. The sequence controller 31 inputs the raw datato the sequence controller control unit 41. The sequence controllercontrol unit 41 stores the raw data in the k-space formed in the k-spacedatabase 42 as k-space data.

Note that in parallel with the aforementioned pulse sequence andreception of the NMR signal from the object P (data acquisitionoperation), acquisition of a respiratory gating signal or an ECG signalfrom the object P or monitoring of the body motion of a predeterminedportion of the object P may be performed.

Then, in step S3, the CSF image generating unit 43 obtains the k-spacedata from the k-space database 42, performs data processing includingthe image reconstruction processing on the k-space data, and generatesthe time-series CSF image data. Note that if, in step S2, the regionnon-selective IR pulse is applied before the application of the labelingpulse, the REAL reconstruction processing is used as part of the imagereconstruction processing in step S3.

FIG. 9 illustrates an example of the CSF image imaged by the magneticresonance imaging apparatus 20 illustrated in FIG. 3.

FIG. 9 illustrates the CSF image at a time of being acquired withapplication of the DANTE pulse. It can be confirmed that a stripepattern is generated by the DANTE pulse. It can also be confirmed thatthe stripe pattern also moves with the CSF flow. It is possible toperform display processing on the CSF image data so as to better observethe dynamic CSF behavior from the CSF image.

In this case, in step S4, the display processing unit 44 performsdisplay processing on the CSF image data and displays the CSF image dataon the display device 34 after the display processing.

FIG. 10 illustrates an example of a distinguishably (identifiably)displayed CSF obtained by performing display processing on the CSF imageillustrated in FIG. 9. More specifically, signal inversion processing isperformed on the data of the CSF image illustrated in FIG. 9 to invertthe grayscale. Further, a signal threshold corresponding to the CSFregion is set and coloring is performed on the CSF region extracted bythe threshold processing. Then the CSF is distinguishably displayed moreclearly. Note that the region having continuity in terms of signalintensity compared with the position extracted as the CSF region by thethreshold processing may be re-extracted (expanded) as the CSF regionwith the use of a region growing algorithm, and then coloring may beperformed on the re-extracted CSF region. The region growing algorithmis such that a determination is made as to whether a pixel locatedadjacent to the start point satisfies preliminarily specifiedconditions; if the conditions are satisfied, the adjacent pixel isdetermined to belong the same region; and this operation is repeated toextract the entire target region.

FIG. 10 illustrates the image in which CSF is made distinct by coloringthe CSF region re-extracted by the region growing algorithm, ingrayscale (achromatic color) for the sake of convenience.

In addition, it is possible to observe the flowing behavior of CSF asmotion pictures like a cine image by displaying a plurality of CSFimages each corresponding to a different data acquisition time inchronological order. Further, the detailed dynamic CSF behavior which isa portion to be observed can be easily understood by the color images.In this operation, it is desirable to display information on “which timephase of the respiration, heartbeat or body motion imaging time of eachframe corresponds to” in parallel with each frame image, if acquisitionof a respiratory gating signal or an ECG signal or monitoring of thebody motion is performed in step S2.

Moreover, with the elapse of time from the imaging start time, thecoloring criteria may be changed for each frame. As an example, considerthe case where the SPAMM pulse is used as the labeling pulse and theregion non-selective IR pulse is not applied before the labeling pulse(see FIG. 7C). Immediately after the labeling pulse as a saturationpulse is applied, the difference in longitudinal magnetization componentMz between the labeled CSF (whose longitudinal magnetization componentMz is close to zero) and the unlabeled CSF becomes large and thedifference in NMR signal level therebetween also becomes large. As thetime has elapsed since the labeling pulse was applied, the longitudinalmagnetization component Mz of the labeled CSF also gradually recovers tothe static magnetic field direction, and the difference in NMR signallevel between the labeled CSF and the unlabeled CSF becomes small.

Here, assuming that white corresponds to 100% in grayscalerepresentation and black corresponds to 0% in grayscale representation,the NMR signal from the unlabeled CSF is close to a highest signal levelregardless of the data acquisition time and is displayed, for example,as a grayscale value of about 100% (white) in the CSF image. Incontrast, the NMR signal from the labeled CSF is displayed, for example,as a grayscale value of about 0% (black) in a frame of an earliest dataacquisition time, because its signal level is close to the lowest.However, the NMR signal from the labeled CSF is displayed, for example,as a grayscale value of about 50% (gray) in a frame of a late dataacquisition time, because its signal level is increased by the recoveryof the longitudinal magnetization component Mz.

Then, image processing is performed so that the labeled CSF is displayedcommonly, for example, as yellow in all of the frames; and the unlabeledCSF is displayed commonly, for example, as red in all of the frames; andthe extracted CSF region is displayed, for example, only in a colorrange from red to yellow. In this case, a grayscale value of 0% isdisplayed in yellow in the frame of the earliest data acquisition time;and the later the data acquisition time of one frame is, the higherpercentage of grayscale value corresponding to yellow is allotted to theone frame. At the same time, a grayscale value of 100% is made tocorrespond to red regardless of the data acquisition time. The aboveimage processing allows the labeled CSF to be displayed in the samechromatic color commonly in all of the frames, and thus the CSF behaviorcan be visually distinguished in an easy manner.

FIG. 11 illustrates another example of a distinguishably displayed CSFobtained by performing display processing on the CSF image data imagedby setting the labeling region to a stripe pattern.

FIG. 12 illustrates an example of a distinguishably displayed CSFobtained by performing display processing on the CSF image data imagedby setting the labeling region to a grid pattern.

FIG. 13 illustrates an example of a distinguishably displayed CSFobtained by performing display processing on the CSF image data imagedby setting the labeling region to a radial pattern.

In FIGS. 11, 12 and 13, the CSF image is displayed in black and whitegrayscale. However, in fact, in FIGS. 11, 12 and 13, the completelyblack regions are displayed in yellow as the labeled CSF, and the grayregions are displayed in red as the unlabeled CSF.

As illustrated in FIGS. 11, 12 and 13, it can be confirmed that patternseach labeled as a stripe, grid or radial shape are formed through theentire image. The labeled CSF displayed in yellow is out of the labelingpattern region labeled as the stripe, grid or radial shape. From theabove fact, it can be confirmed that the CSF is moving.

FIG. 14 illustrates another example of a distinguishably (identifiably)displayed CSF obtained by performing the same display processing as inFIG. 11 on the CSF image data imaged by setting the labeling region to astripe pattern. FIG. 14 enlarges the CSF portion in the head (centerportion of the image in FIG. 11). FIG. 14 displays a plurality of CSFimages each corresponding to a different time in chronological order (asFIGS. 14A and 14B), when imaging is performed by acquiring therespiratory gating signal in step S2. FIG. 14A corresponds to the imageobtained at a data acquisition timing (imaging time) T1, and correspondsto the exhalation time phase. FIG. 14B corresponds to the image obtainedat a data acquisition timing (imaging time) T2, and corresponds to theinhalation time phase. In this example, T2 is later than T1 in terms oftime.

FIG. 15 illustrates an example of a plurality of CSF images eachcorresponding to a different imaging time displayed in chronologicalorder in the same manner as in FIG. 14, when monitoring is performed onthe abdominal motion in step S2. FIG. 15A corresponds to the imageobtained at a data acquisition timing (imaging time) T3, and correspondsto the exhalation time phase. FIG. 15B corresponds to the image obtainedat a data acquisition timing (imaging time) T4, and corresponds to theinhalation time phase. In this example, T4 is later than T3 in terms oftime.

Although the CSF image is displayed in grayscale in FIGS. 14 and 15, infact, the completely black regions (‘black parts’ as shown in FIGS. 14and 15) are displayed in yellow as the labeled CSF, and the gray regions(‘gray parts’ as shown in FIGS. 14 and 15) are displayed in red as theunlabeled CSF in FIGS. 14 and 15.

As illustrated in FIGS. 14 and 15, it is desirable to displayinformation on “which respiration time phase imaging time of each framecorresponds to” under each frame image.

In FIG. 14A, the CSF flow rate can be calculated by detecting how farthe CSF of specific portion labeled by a pattern such as a stripe movesin the CSF image in the frame of FIG. 14B and by dividing the movingdistance by the time difference (T2−T1) in imaging time between the twoframes. In FIG. 15, the CSF flow rate can be calculated in the samemanner.

(Advantages)

As described above, the magnetic resonance imaging apparatus 20according to the present invention applies a labeling pulse (after aregion non-selective IR pulse is applied or without applying the regionnon-selective IR pulse), consecutively acquires CSF image data of aplurality of frames, each corresponding to a different imaging (dataacquisition) time, performs display processing such as coloring on theCSF image data, and distinguishably displays the CSF. More specifically,labeling is performed once, and then data acquisition corresponding toeach frame of CSF image is consecutively (continuously) performed.Consequently, the labeled CSF is the same for each frame. Therefore, CSFimage data allowing the dynamic CSF behavior to be easily understood canbe acquired. Moreover, a wide range of dynamic CSF behavior can becontinuously depicted.

Clinically expressed, when the CSF is not moving, its state of beingstopped can be surely determined. In the case of a normal CSF, it ispossible to visualize how the CSF moves. For example, hydrocephalus andsubarachnoid hemorrhage indicate that the CSF does not move and may havesimilar symptoms, but are different in the portion where the CSF doesnot move. Therefore, according to the magnetic resonance imagingapparatus 20, hydrocephalus and subarachnoid hemorrhage can bedistinguished.

In addition, according to the magnetic resonance imaging apparatus 20,the dynamic CSF behavior can be understood, and thus the CSF flow ratecan be measured. Specifically, the CSF flow rate can be calculated bydetecting how far the CSF of specific portion labeled by a pattern suchas a stripe moves in the CSF image in the next frame and by dividing themoving distance by the time difference in imaging (data acquisition)time between the two frames.

Further, unlike the conventional t-SLIP method, a plurality of BBTIsneed not be set, and thus image data without a time difference can beacquired.

Note that the magnetic resonance imaging apparatus 20 allows any fluidssuch as blood other than the CSF to be imaged in the same manner. Inparticular, the magnetic resonance imaging apparatus 20 is suitable forimaging non-periodic fluids.

What is claimed is:
 1. A magnetic resonance imaging (MRI) apparatuscomprising: a magnetic resonance (MR) data acquisition unit whichconsecutively acquires a plurality of MR data sets from a region ofinterest, each acquired MR data set corresponding to a different dataacquisition time, after a labeling pulse is applied to a region ofinterest without applying any labeling pulse between the consecutivedata acquisitions and without substantial time delay between theconsecutive data acquisitions; and a cerebrospinal fluid (CSF) imagedata generation unit which generates a plurality of CSF image data setsbased on the plurality of MR data sets, wherein each CSF image data setcorresponds to a respective one of the MR data sets.
 2. The MRIapparatus according to claim 1, wherein the MR data acquisition unit isconfigured to apply a saturation pulse as the labeling pulse.
 3. The MRIapparatus according to claim 2, wherein the MR data acquisition unit isconfigured to apply a region non-selective inversion recovery pulsebefore the labeling pulse is applied.
 4. The MRI apparatus according toclaim 3, wherein the CSF image data generation unit is configured togenerate the plurality of CSF image data sets using REAL reconstructionprocessing.
 5. The MRI apparatus according to claim 1, furthercomprising: a display processing unit which performs display processingto distinguishably display a CSF region in the plurality of CSF imagedata sets.
 6. The MRI apparatus according to claim 1, furthercomprising: a monitoring unit which monitors a periodic body motion ofan object in a period while the plurality of MR data sets are beingconsecutively acquired; and a display processing unit which generatesand displays a plurality of CSF images based on the plurality of CSFimage data sets, and displays information on timing of the body motionwith respect to the acquisition time of MR data sets for each of theplurality of CSF images, based on monitoring results of the monitoringunit.
 7. The MRI imaging apparatus according to claim 1, wherein the MRdata acquisition unit is configured to apply a time spatial labelinginversion pulse as the labeling pulse.
 8. The MRI imaging apparatusaccording to claim 1, wherein the MR data acquisition unit is configuredto apply a SPAMM (spatial modulation of magnetization) pulse or DANTE(delays alternating with nutations for tailored excitation) pulse as thelabeling pulse.
 9. The MRI imaging apparatus according to claim 1,wherein the MR data acquisition unit is configured to selectively applythe labeling pulse to a stripe patterned region or a grid patternedregion of the CSF to be imaged.
 10. The MRI imaging apparatus accordingto claim 1, wherein said MR data acquisition unit is configured toselectively apply the labeling pulse to a radial patterned region of theCSF to be imaged.
 11. The MRI apparatus according to claim 1, furthercomprising: a calculation unit which extracts each of plural regions ofCSF by performing threshold processing on each of the plurality of CSFimage data sets; then detects a moving distance of the CSF labeledbetween the plurality of CSF image data sets; and calculates a flow rateof the CSF based on the moving distance and interval of acquisitiontimes of the plurality of MR data sets corresponding to said image datasets.
 12. The MRI apparatus according to claim 1, wherein the MR dataacquisition unit is configured to simultaneously apply the labelingpulse to a plurality of regions.
 13. A magnetic resonance imaging (MRI)apparatus comprising: a magnetic resonance (MR) data acquisition unitwhich consecutively acquires a plurality of MR data, each correspondingto a different data acquisition time, after a labeling pulse is appliedto a region of interest; and a cerebrospinal fluid (CSF) image datageneration unit which generates a plurality of CSF image data based onthe plurality of MR data so as to correspond to each of the plurality ofMR data; a calculation unit which extracts each of regions of CSF byperforming threshold processing on each of the plurality of CSF imagedata; then detects a moving distance of the CSF labeled between theplurality of CSF image data; and calculates a flow rate of the CSF basedon the moving distance and interval of acquisition times of theplurality of MR data.
 14. A magnetic resonance imaging (MRI) methodcomprising: applying a magnetic resonance (MR) labeling pulse to aregion of interest; consequently acquiring a plurality of MR data setsfrom said region of interest, each acquired MR data set corresponding toa different data acquisition time, after the labeling pulse is appliedto said region of interest without applying any labeling pulse betweenthe consecutive data acquisitions and without substantial time delaybetween the consecutive data acquisitions; and generating a plurality ofcerebrospinal fluid (CSF) image data sets based on respectivelycorresponding ones of the plurality of MR data sets.